1. Field of the Invention
The present invention relates to a rear mount structure of an engine, and more particularly, to a rear mount structure of an engine for fixing a rear mount member.
2. Description of the Related Art
In a vehicle, as shown in FIG. 6, when an engine 108 of a power train 107 to be mounted is of a longitudinal layout, a pitch mount type in which the power train 107 is supported at three locations, i.e., a right mount portion 112 and a left mount portion 113 of the engine 108 and a rear mount portion 114 at a rear end of a transmission 109 is employed in some cases. In this case, a rear mount member 115 is required for supporting the rear mount portion 114. It is necessary that the rear mount member 115 is of a structure that is not easily vibrated. To prevent a vibration from being transmitted to a vehicle body, the rear mount member 115 is generally mounted on lower portions of a pair of side frames which are disposed on both sides of the vehicle in its widthwise direction and which form a framework of the vehicle body.
According to a vehicle body structure of an automobile concerning the rear mount of Japanese Patent Application Laid-open No. 1-126885, in a periphery of a mounting portion of a rear portion of an engine, a mounting member is joined to a rising portion of a tunnel of a floor panel in a longitudinal direction of the vehicle, a mounting portion which supports an end of the engine is provided on this mounting member, and an outrigger is mounted on a position crossing the mounting portion such that the outrigger extends between the mounting member and the side member (side frame), and loads applied to various portions are reduced.
According to an engine rear mount structure of Japanese Patent Application Publication No. 60-48361, a connecting member which is a separate member from a cross member is provided between both sides of a tunnel of a floor panel, the connecting member is rigidly connected to lower ends of bolts on both sides of the tunnel in the widthwise direction of the vehicle, and the connecting member is supported such that it is sandwiched between a head of a bolt and a mount insulator which supports a transmission that is integral with the engine on a cross member in an axial direction of the vehicle.
In the case of the structure in which the rear mount member 115 is mounted on the lower portions of the side frames disposed on both sides of the vehicle in its widthwise direction, there is a problem that the length of the rear mount member 115 is increased, the weight thereof is also increased and its rigidity is deteriorated.
In the case of a vehicle requiring high off-road performance, target values of the ground height (road clearance) and the lamp brake over angle are high. Therefore, in the case of the off-road vehicle, it is necessary to set the ground height at a high level.
When the rear mount member is fixed to the side frames, however, as shown with two-dot-chain lines that are added to FIG. 4 of the invention, at least the rear mount member 115 is disposed below the vehicle lower than the side frames by the height h. Therefore, the ground height is reduced. In order to secure the ground height, there exist some measures, e.g., the side frames are moved upward with respect to the vehicle, but there are problems that a living space in the passenger room becomes narrow correspondingly and a vehicle barycenter becomes high, and it is desired to improve the structure.
That is, in the conventional technique, since the rear mount member is fixed to the side frames, the length of the rear mount member is increased in the widthwise direction of the vehicle, and the weight of the rear mount member is increased. Further, since the length of the rear mount member is increased and its rigidity is low, a floating structure which fastens the rear mount member such that a vibration is not propagated to a floor panel through a rubber bush is merely employed.
In the case of the off-road vehicle, it is necessary to set the ground height at a high level. Since the rear mount member is fixed to the side frames, at least the rear mount member is disposed below the vehicle lower than the side frames. Thus, a layout of the vehicle in the vertical direction is limited due to a relation of the ground height, and there is a problem that the design flexibility is deteriorated.